1. Field of the Invention
The present invention relates to a reciprocating compressor, and particularly, to a motor structure for a reciprocating compressor by which power lowering of a motor generated by a phenomenon that a piston is backward moved when a fluid is compressed can be prevented.
2. Description of the Background Art
Generally, a compressor is a device for compressing fluid such as refrigerant gas. The compressor can be classified into a rotary compressor, a reciprocating compressor, and a scroll compressor.
The compressor comprises: a sealed chamber, a motor installed inside the chamber for generating driving force when an electric source is applied from outer part, and a compression part for performing compressing operation of the fluid by being applied the driving force of the motor.
FIG. 1 is a partial cross-sectional view showing a motor of a reciprocating compressor according to the conventional art.
The motor of the reciprocating compressor according to the conventional art comprises: an outer core 102 of cylindrical form fixed inside the chamber (not shown); an inner core 106 disposed with a predetermined gap between an inner circumferential surface of the outer core 102 and fixed on an outer circumferential surface of a cylinder 104; a winding coil 108 wound on inner side of the outer core 102 and being applied the electric source from outer part; and a magnet 110 disposed between the outer core 102 and the inner core 106 with a predetermined intervals for performing linear reciprocating movement when the electric source is applied to the winding coil 108.
The outer core 102 includes a opening recess 112 formed in circumferential direction so that the winding coil 108 is disposed on an intermediate portion of the inner circumferential surface of the outer core 102, and a path portion on which flux flows when the electric current is applied on the winding coil 108 is formed in boundary direction of the opening recess 112. Both end parts of the inner circumferential surface of the outer core 102 which is divided by the opening recess 112 form a pole part 114.
The inner core 106 is formed as a cylinder fixed on the outer circumferential surface of the cylinder 104, and a length of the inner core 106 is formed to be same as that of the outer core 102.
A plurality of magnet 110 are disposed on a magnet holder 116 which is located between the inner core 102 and the outer core 106 in circumferential direction with a certain intervals therebetween. An center part of the magnet 110 is disposed to be in a same line (M) with a center part of the outer core 102, and the both end parts of the magnet 110 are disposed to be located on intermediate parts of the pole part 114.
The magnet holder 116 is integrally connected to a piston 120 which is disposed to perform linear reciprocating movement inside the cylinder 104, and thereby, when the magnet 110 undergoes the reciprocating movement, the magnet holder makes the piston 120 perform the reciprocating movement with same strokes as the magnet 110. In addition, return springs (not shown) are installed on both sides of the magnet holder 116 for providing an elastic force when the piston 120 performs the reciprocating movement, and for setting the location of the magnet holder 116 to the original position when the motor is stopped.
At that time, a maximum stroke of the piston 120 is decided within a range of interaction between a flux generated from the magnet 110 and a flux generated between the outer core 102 and the inner core 106.
A compression part 118 is installed on an end part of the cylinder 104 for performing the compressing operation of the fluid according to the reciprocating movement of the piston 120.
As shown in FIG. 2, according to the conventional motor of the reciprocating compressor, when the electric power is applied to the winding coil 108, the flux is formed around the winding coil 108 and the flux forms a closed loop along with the outer core 102 and the inner core 106. And the magnet 110 is linearly moved to axial direction by the interaction between the flux generated between the outer core 102 and the inner core 106 and the flux generated by the magnet 110.
In more detail, the magnet 110 maintains its initial mid position by the elastic force of the return spring when the motor is in stopped state, and the both end parts are located on intermediate parts of the path portion 114.
In that state, when the electric current is applied on the winding coil 108 to one direction, the flux formed between the outer core 102 and the inner core 106 is flowed to A direction in FIG. 2. Then, the magnet 110 is linearly moved to C direction in FIG. 2 by the interaction with the flux formed between the outer core 102 and the inner core 106, and accordingly, the piston 120 is moved forward to perform the compression operation of the fluid.
In addition, when the electric current is applied on the winding coil 108 to the other side, the flux formed between the outer core 102 and the inner core 106 is flowed to B direction in FIG. 2. Then, the magnet 110 is linearly moved to D direction in FIG. 2 by the interaction between the flux flowing between the outer core 102 and the inner core 106 and the flux formed by the magnet 110, and accordingly, the piston 120 is retrieved to suck the fluid.
Herein, in case that the reciprocating compressor is operated in that ideal condition, the magnet 110 is reciprocatingly moved within the stroke (P) range, however, in actual operation of the motor, the piston 120 may be moved to the opposite direction of the compression part 118 by difference between the compression pressure and the sucking pressure of the fluid, and then, the magnet 110 is reciprocatingly moved within an actual stroke (Q) range out of the ideal stroke (P) range.
As described above, if the mid position of the magnet is escaped from the initial mid position, the power of the motor is lowered and motor saturation may be generated. In addition, if the magnet deviates from the pole part, the system becomes unstable and it can not be controlled.